String Lights on Trees

So it was Christmas and the Detectives were invited to a friend's house. Well, in summary that friend was a Christmas decoration fiend that puts up string lights EVERYWHERE. Around the inflatable Santa, on fake Fir trees, on real maple tree branches, etc. (foreshadowing). After hanging out for a while, cue the crashing of a 15 cm (diameter) sugar maple branch onto the roof. Upon examining the broken end of the branch, the detective noticed a doughnut-shaped break pattern. A relatively smooth and discoloured outer ring made up one-third the diameter of the branch, and the middle two-third was splintered wood (at the centre).

His friend's tradition of putting on string lights and leaving them wrapped spirally around branches have predisposed them to failure. A few inches back from the break was the torn end of string lights with frayed wires exposed. But that wire was sticking out from the inside of the branch. Over time as branches grew, they became girdled, and new wood were deposited over the string lights.
However, string lights could be left up for long periods of time by attaching them vertically along the trunk or axially along the branches.

As for existing string lights completely swallowed up by the wood growth, just cut the wires flush to the bark and leave the lodged wires. If they were to be dug out, it might create an even greater problem. The friend could also - after consultation with an arborist - consider to prune off branches, which have fully impounded wires that would girdle.